Photoconductive copy system



Oct. 17, 1967 P. G. KALMAN PHOTOCONDUCTIVE COPY SYSTEM Filed March 27, 1964 JIT'IG 32. 35

26 ll/ 74j ITL FIG. 4

INVENTOR PETER G. @LMA/V BY @Q07 MMV/m United States Patent Olii-ice 3,347,669 Patented Oct. 17, 1967 3,347,669 PHOTOCONDUCTIVE CPY SYSTEM Peter G. Kalman, Loudon, England, assignor to A. B. Dick Company, Niles, Ill., a corporation of Illinois Filed Mar. 27, 1964, Ser. No. 355,168 22 Claims. (Cl. 96-1) ABSTRACT F THE DISCLOSURE Specification This invention relates to a system for the production of copy. In particular, the invention is concerned with a copy process from which single, or multiple, copies can lbe produced from an original and wherein photoconductive layers are employed in the course of the processing.

The use of photoconductive dielectric layers for copy production is well known, this technique being employed in the so-called Xerox process. In this process, an electrostatic charge is applied to the surface of a photoconductive dielectric layer disposed on a conductive body by corona discharge from a high potential source. The charged surfaces which are formed are exposed to light or other radiations through an image whereby the electrost-atic charge is destroyed in the exposed surface portions. This leaves an electrostatic latent image on the surface which can be developed through the use of pigment powders. In most instances, the powder is transferred to a copy sheet for image development and setting of the powder thereon, thereby providing a permanent copy.

A different technique referred to as the Videograph process is described in Patent Nos. 3,075,859, 2,996,573 and 2,879,422. In this technique, an original is scanned by suitable scanning means adapted to generate an electrical signal which can then be transmitted to a cathode ray tube. This tube emits a discharge from wires extending through the face of the tube for disposition of an electrostatic charge on a dielectric writing medium. This medium is displaced between the face of `the tube and a suitable ground whereby -a latent electrostatic image corresponding to the original is formed on the surface of the dielectric writing medium. Instead of receiving its signals from the scanner, the cathode ray tube may be signaled by electronic read-out devices from electronic data storage means and the like. The electrostatic image can be developed by dry powder techniques or through the use of toner carried in a liquid medium.

An additional electrostatic printing technique which has been developed involves the use of elements referred to as electrets. Electrets comprise material capable of internal polarization for ultimate development of an electrostatic image which is characterized by volumetric eifect rather than the surface eifect of the Xerox process. In this technique, a latent electrostatic image is developed which decays less lrapidly than the decay which characterizes the corona effect of the Xerox process. This arrangement permits better image development and better image retention for the production of one or more copies of operation for each copy.

In accordance with this more recent development, de-

scribed in an article entitled Data Storage and Display With Polarized Phosphors by H. P. Kolman and I. Rennert, Electronics, August 28, 1959, pages 39-41, Ian electret is found having a latent electrostatic image by exposure of a phosphor body to a DC field with simultaneous radiation to cause internal polarization of the phosphor.

The ramifications appear possible with the system described, one of which may be used to for-m a positive image and the other of which may be used to form a negative image, either of which can be read out with suitable electroni-c reading equipment or either of which may be developed by colored powder development techniques, Ias in the Xerox process, for the production of visible copy either on the electret or on copy paper in response to transfer of either the electrostatic image or the powder image from the electret.

In one ramification image formation is accomplished by selective radiation of locations of the phosphor body while an over-all external DC field is applied by a potential of -about 50-500 volts. This causes internal polarization corresponding to the portions radiated to develop the charged latent electrostatic image which is retained for image development, In the other ramiication, internal `polarization is provided through the phosphor body by application of the DC voltage simultaneously with uniform radiation of the phosphor. Thereafter the image is written in the phosphor by selective irradiation in the absence of an extern-al DC field. This subsequent radiation destroys internal polarization in the exposed areas to leave an electrostatic latent image which can be developed.

The system described is sensitive to temperature and humidity conditions from the standpoint of the rate of decay of the image and the image that is developed lacks somewhat in intensity by reason of the relatively low charge of polarization generated in the latent image.

Further, the combination of irradiation simultaneously with exposure of the electret to the external DC eld complicates the process and the equipment with which the process can be performed.

In copending `application Serial No. 333,540, filed December l26, 1963, and entitled Electro-Electret and Method for Imaging Same, there is described a system which overcomes the disadvantages recognized with prior systems utilizing electrets. The improved system involves Ia method for producing dry copy which includes the steps of exposing Ya phosphor layer between electrodes and generating a high intensity DC field between the electrodes. The system provides for the attraction of electrons toward one surface of the phosphor layer and thereafter the charged phosphor layer is exposed to radiations in selected areas to remove the charge in the exposed Iareas and to leave a latent electrostatic image in the non-exposed areas.

The instant invention has for its object the provision of a still further system for dry copy processing wherein photoconductive surfaces are utilized for the formation of electrostatic image areas.

It is an additional object of this invention to provide a copying technique which is highly efficient from the standpoint of materials employed and from the standpoint of the steps necessary for conducting the technique.

It is a still further object of this invention to provide a copy system which permits the production of single or multiple copies of high quality.

These and other objects of this invention will appear hereinafter and for purposes of illustration but not of limitation, specific embodiments of this invention are shown in the accompanying drawing in which:

FIGURE l is a diagrammatic cross sectional view illustrating an assembly employed inthe practice of this invention;

FIGURE 2 is a diagrammatic cross sectional view illustrating an alternative assembly;`

FIGURE 3 is a diagrammatic cross-sectional View illustrating one arrangement which can be employed during radiation exposure; and,

FIGURE 4 is a diagrammatic plan view illustrating a latent image formed in accordance with the techniques of this invention.

Itis observed that when a phosphor layer (eg. zinc cadmium sulphide) supported on a semiconductive base such as paper, is disposed between polarizable dielectric sheets such as polyethylene terephthalate and an electrical field of a suitably high magnitude `is applied in darkness and then reversed across the assembly, a brief luminescent ash occurs at the instant of the reversal of the field. At least one` of the conductive electrodes situated outside the assembly described, by means of which the field is applied to the assembly, must bevtransparent if` this luminescence is to be observed (e.g. brine in a transparent container may be used).

The phosphor-coated paper is found to be electrically charged when extracted from between the insulating dielectric sheets after the occurrence of the luminescence, even though the electrical resistance of the insulators employed is sufficiently high to prevent the passage of a leakage current through the charging assembly. The coated paper so charged may then be exposed to a pattern of illumination so that it will become selectively discharged in the lit areas but will retain its charge in the dark areas, and the latent image so produced can be made visible by applying a suitable electroscopic powder dispersed in a solid or liquid carrier medium as already known in the art and the powder pattern may either be affixed to the coated paper by heat or transferred from it by mechanical pressure or electrical field to, for example, a plain paper copy sheet. Since the phosphors which are most efficient when charged according to the present invention are more costly than plain paper and are also not white in color and hence objectionable when directly utilized:as the copy to be produced, it is preferred to place athin insulating overlayer such as Mylar upon the charged phosphor layer and electroscopic powder may be applied to this overlayer in the same way as described above; the powder pattern so produced .may be permanently affixed to the `overlayer by heat or a protective lacquer, or it may be transferred from it to a plain paper copy sheet by mechanical pressure or electrical field or both.

The method of the invention utilizesrnaterials capable of luminescence when subjected to a reversed DC or alternating electrical field, such as a thin air layer situated between and acting in conjunction with polarizable dielectric insulatorsteg. polyethylene terephthalate) between which a phosphor-coated substrate (e.g. paper) to be charged is also disposed during` the charging process, It is, however, to be understood that any materials capable of such activating luminescence when subjected to a reversed DC or alternating electrical field (e.g. electroluminescent grade zinc cadmium sulphide doped with copper, or like materials) are intended to be included within the scope of the invention.

The presence of the coated substrate to ber charged within the charging assembly is found to vbe necessary only during the brief period of the activating luminescence although it is found that the electrical fields applied before and after luminescence have no deleteriouseffect upon it with many of the phosphors suitable for the process presently disclosed. Furthermore, it is found when such phosphors are employed that it is immaterial whether the coated paper to be kcharged is illuminated or not prior to the luminescence caused by the reversal of the field; however, the coated substrate is found to be radiationsensitive following the luminescent flash and may be surfacewise selectively irradiated either within the charging assembly with the electrical field applied (if at least one electrode is transparent to the radiation employed) or, alternatively, it may also be selectively irradiated outside the chargingy assembly.

Substances comprising phosphor materials are considered particularly suitable for the practice of this invention. Such materials, many of which are disclosed in detail in published literature on electrets, readily provide the desired charged surfaces whic'hare photosensitive and otherwise sensitive to radiations whereby latent images can be easily formed. ,Suitable materials comprise for example, Sylvania phosphors types 110, and 122.

FIGURE 1 of the drawing illustrates an assembly 10 of the type which `can be employed in the practice of this invention. The assembly includes upper and `lower electrodes 12 and 14 and each electrode is provided with a tab 16 for connection of lead wires 18. Intermediate the electrodes, there is provided a member 20 which includes a base 22 and a coating 24. The base comprises a semiconductive dielectric such as paper while the coating comprises a photoconductive layer adapted to provide a charged surface.

Inter-posed between the member 20 and the electrodes are insulators 26 and 28. In the use of an assembly of the type illustrated, the members are preferably in,

contact whereby a thin sandwich is provided. The drawings illustrate the members in spaced apart relationship to provide a convenientpicture of the desired arrangement.

The method of this invention comprises the formation of a high intensity DC field between conductive electrodes 12 and 14. Thereafter the field is changed to an extent necessary to cause luminescence within the sandwich assembly. The layer 24 on the member 20 reacts in response,

to the luminescence whereby a charged surface will be formed on the layer,

FIGURE 2 illustrates` an arrangement including a member 30 disposed between electrodes 32 and 34. These electrodes each include tabs 36 and leads 38 whereby a DC field can be generated between the electrodes. The member 30 includes a dielectric base portion 40, a first layer42 comprising the chargeable material and a second layer 44 comprising an electroluminescent material. The generation of a high intensity DC field followed by a change in this field will cause the material 44 to luminesce and will cause -the material 42 `to bec-ome charged.

The arrangements shown in FIGURES l and 2 comprise two alternatives available for the practice of this invention. It will also be understood that various other arrangements could be employed which achievethe same or similar results. For example, the electroluminescent material could be dispersed within the chargeable material, and a single layer could be formed on a base. It is also preferredthat insulating means be interposed between the electrodes and the member to be charged, and

'one or both of these may also be made of a suitable insulating-electrically luminescent material. Glass platesk could also beutilized in the assembly as described in copending application Serial No. 333,540.

FIGURE 3 illustrates an assembly which may be employed for imaging a charged member 20 which has been charged in an assembly of the type shown in FIGURE 1. The charged layer 24 is adaptedto l-ose its charge when exposed to suitable radiations, for example visible or ultraviolet radiations. Such radiations maybe provided` through the use of a light source illustrated at 46. The light rays 48 `are directed on to a negative 50 which includes areas adapted to transmit light in varying degrees. The charged surface 24 when exposed in certain areas will have a latent image formed thereon.

FIGURE 4 illustrates the member 20 with the latent image 52 illustrated in broken lines. The latent image can be developed by dusting with a suitable -pigment powder in a thermoplastic resinous base. This procedure, described in Patent No. 3,060,051, involves attraction of the pigment powder to the unexposed charged areas in amounts proportional to the density of the charge. Alternatively, the image can be developed through the use of a suspension of pigment powder in a liquid carrier as described in Patent No. 2,907,674.

The pigment powder on the developed im-age can be set directly on the member 20 by heat or by solvent techniques to provide a permanent copy, or the image could be transferred to a copy sheet or to a duplicating master. Transfer could be effected by reversal of the electrical field with copy paper in contact with the developed image or transfer could be effected by a preferential attraction or 4adhesion of the image t-o a copy sheet. Alternatively, the pigment powder may be deposited by the same means onto a dielectric overlay, such as a thin film or polyethylene terephthalate disposed in intimate contact with the member during the pigment deposition. The image may be affixed to this overlay or transferred from it onto a copy sheet by pressure or by electrical field.

It will be understood that the instant invention is not limited with regard to any techniques employed in the preparation of copy. The invention is primarily directed to a unique method for the formation of an electrostatically charged surface, which surface will lend itself toa wide variety of copy techniques. The natureof the electrodes employed in the construction is not critical provided they are suitable for applying a DC field of sufficient magnitude and provided they are capable of operating for changing the DC field to effect the necessary luminescence. It is contemplated that brine electrodes coul-d be employed so that the assembly will be visible through the electrode where observation is desired. This arrangement is convenient where the luminescence occurring is to be observed. Such electrodes are also contemplated for use where radiations are to be directed at the charged layer during or shortly after the luminescence whereby the latent image can be formed without moving the charged layer from between the electrodes. It will be apparent that any suitable electrodes could be employed since the transparent electrodes are only desired in limited circumstances. The layer of chargeable material which forms the active surface may be selected from any of the phosphor materials disclosed in conjunction with the formation of electrets. Zinc cadmium sulphide is considered to be highly suitable or use in an application of the type described. Other materials such as sulphur, anthracene, selenium and the like are also contemplated. It is preferred that the layer be doped by the addition of a small amount of silver, copper, chlorine or the like which is uniformly distributed throughout the layer. As disclosed in the aforementioned copending application Serial No. 333,540, it is sufficient to make use of a doping agent in an amount within ythe range of 0.1 to 2.0 percent by weight of the layer. The preferred range is between 0.4 and 0.6 percent by weight of the coating solids. The dope may be incorporated by addition to the slurry of the dielectric mat-erial in a suitable carrier or it can be sprayed onto the particles for uniform distribution.

It will be understood that the instant invention contemplates the use of any material which may be energized by the luminescence whereby a charged surface can be produced. Activated or doped semi-conductor materials are considered to be a logical category for the selectionrof the chargeable materials.

A highly suitable insulating dielectric material comprises polyethylene terephthalate. Rea-dily obtainable thin films of this material have highly satisfactory insulating characteristics whereby they can be readily incorporated r 6 as one or both of the insulating sheets 26 and 28 employed in the assembly of FIGURE 1.

Other suitable materials comprise acetate films and Mylar films, the latter being closely related to the polyethylene. It will be understood that various materials are capable of luminescence when excited by changing electrical fields under different conditions. Accordingly, the instant invention should not be limited to specific materials since any electrically luminescent material is contemplated. Some materials in this category may be impractical for use due to the conditions necessary to effect electroluminescence; however, various magnitudes of voltage and ranges of various changes are considered to be within the scope of this invention.

It is to be understood that paper is not the only substratum for the purposes of the present invention but that any other suitable semiconductive or partially or slightly conductive medium is also intended to be included. It is, furthermore, possible to omit one of the insulators, for example that denoted by 28- in FIGURE l and the phosphor layer 24 to be charged may also be directly deposited, with or without the semiconductive layer 22, onto one of the conductive electrodes, in this instance Ithat denoted by 14. It is to be understood also that the charging assembly described need not necessarily conform to a plane geometry but that curved, for example cylindrical or barrel-shaped, configurations of the layers described may also be employed to good effect and are intended to be included within the scope of the invention.

The following will illustrate suitable techniques for the practice of this invention:

EXAMPLE l 10 parts by weight Sylvania type 122 phosphor 7 parts by weight General Electric Sli-82 resin In the above formulation the Sylvania type 122 phosphor comprises zinc cadmium sulfide which has been doped to contain 0.5 percent by weight silver. The General Electric SR-82 resin is a 60% solution of a curable organo silicon resin of the type ethyl, methyl, phenyl polysiloxane.

The coating composition was applied on a paper base sheet to provide a coating thickness of abo-ut 1.5 mils. 10 mil thick sheets of polyethylene terephthalate were placed on both sides of the coated sheet and a brine electrode was located over the top of .the assembly while an aluminum sheet electrode was disposed on the underside of the assembly.

The sandwich formed between the inner electrode surfaces was about 25 mils in thickness and a DC field of about 200 kv./cm. was generated across .the sandwich. Thereafter, the DC was reversed and a ash of luminescence was emitted upon reversal of the field.

Thev paper base sheet was removed and exposed to selected radiations and thereafter dusted with eleotroscopic powder. The powder adhered strongly to the unexposed areas confirming the presence of an electrostatic charge in these areas.

The presence of .an electrolurninescent film as a laminate on the paper base sheet or the presence of electroluminescent material interspersed in the photoconductive layer or within the insulators employed also produces luminescence in the presence of .the chargeable material whereby this material becomes radiation sensitive and hence suitable for use in electrophotography. It has been found that the change in the field which results in the luminescence need not be undertaken rapidly. Thus, similar results have been observed where the field was gradually reduced in magnitude. Furthermore, the luminescence need not be visible to produce the results of this invention. It will be understood in this connection, the term luminescence is not to be limited to the production of visible radiations. The instant invention is concerned with the production of radiations which can be produced as a result of changing DC field and which will effect electrostatic activation of a chargeable phosphor layer in the manner described. It should also be understood that the invention is concerned with changes in tield in any respect, which changes will cause the luminescence. Reversal of the DC field is not considered a limiting aspect of this invention.

The formation of the charged surface is a consequence ofthe luminescence and, accordingly, the layer of photoconductive material need not be initially present inthe DC field. Some arrangements may be more efiiciently operated wherein the photoconductive layer is brought into the assembly just prior to the field change which effects .the luminescence.

It will be understood that various changes and modifications may be made in the above described system `which provide the characteristics of this invention without departing from the spirit thereof particularly as defined in the following claims.

That which is claimed is:

1. A method `for producing copy comprising the steps of providing an electrically luminescent material, generating a high intensity DC field in the presence of said material, locating a layer of chargeable material in the area` of said luminescent material, reducing the numerical value of the intensity of said field whereby the intensity is changed to the extent that luminescence is generated and wherein said luminescence is effective to electrostatically activate the said layer, exposing the activated layer to radiations in selected areas whereby the charge is removed from the exposed areas to leave a latent electrostatic image in :the non-exposed areas, developing the image with a pigment which is held by the charged areas of the latent electrostatic image and then setting the developed image.

2. A method in accordance with claim 1 wherein the changing of said lield for generating said luminescence is conducted in the dark, and wherein said luminescence is visible to the eye.

3. A method in accordance with claim 1 wherein the changing of said field for generating said luminescence is conducted while the chargeable material is exposed to image forming radiations.

4. A method in accordance with claim 3 wherein the chargeable material is subjected to saidradiations during and afterV the generation of the luminescence.

5. A method in accordance with claim 1 wherein an insulating medium is inserted between said layer and each of the electrodes employed for producing said \DC field during exposure of said layer to said field.

6. A method in accordance with claim 5 wherein at least one of said insulating media comprises said electrically luminescent material.

7. A method in accordance with claim 1 wherein said charged layer is exposed through an original to form a latent electrostatic image in said layer corresponding to said original.

8. A method in accordance with claim 1 wherein said electrically luminescent material is dispersed withinsaid layer.

9. A method in accordance with claim 1 wherein said electrically luminescent material is -ormed as a separate layer located, at least during the charging operation, in contacting relationship with said layer of chargeable material.

10. A method in accordance with claim 1 wherein said electrically luminescent material is formed on one of the electrodes employed for producing said DC field.

11. A method for producing copy comprising `the srteps of providing an electrically luminescent material, generating a high intensity DC field in the presence of said material, locating a layer of chargeable material in the area of said luminescent material, reversing said yDC eld .to change the intensity of said field to the extent that luminescenceis generated and `wherein said luminescence is effective to electrostatically activate the said layer, exposing the activated layer to radiations in selected areas whereby the charge is removed from the exposed areas to leave a latent electrostatic image in the non-exposed areas, developing the image with a pigment which is held by the charged areas of the latent electrostatic image and then setting the developed image.

12. A method in accordance with claim 11 wherein said DC field is repeatedly reversed.

13. A method forproducing an electrostatically charged surface for use in producing copy comprising the steps of providing an `electrically luminescent material, generating a high intensity DC field in the presence of said material, locating a layer of chargeable material in the area of said luminescent material, reducing the numericalvalue of the intensity of said field whereby the intensity is changed to the extent that luminescence is gener-ated, said luminescence being effective to activate the chargeable layer to thereby produce said electrostatically charged layer.

14. A method in accordance with claim 13 wherein the change in said DC field is accomplished by reversing said iield.

15. A method for producing copy comprising .the steps of providingan electrically luminescent material, generating a high intensity DC field in the presence of said material, locating a phosphor layer in the area of said luminescent material, .reducing the numerical value of the intensity of said field whereby the intensity is changed to the extent that luminescence is generated by said luminescent material and wherein said luminescence is effective to charge the said phosphor layer, exposing the charged `layer to radiations in selected areas whereby the charge is removed from the exposed areas to leave a latent electrostatic image in the non-exposed areas, developing the image with a pigment which is held by the charged areas of the latent electrostatic image and the setting the developed image.

16. A method for producing copy comprising the steps of disposing a phosphor layer between electrodes, providing an electrically luminescent material in the area of said phosphor layer, generating a high intensity DC field between said electrodes, reducing .the numerical value of the intensity of said field whereby the intensity is changed to the extent that luminescence is generated by said luminescent material and whereby the said phosphor layer becomes charged by said luminescence, exposing the charged phosphor layer to radiations in selected areas whereby the charge is removed from the exposed areas to leave a latent electrostatic image in the non-exposed areas, developing the image with a pigment which is held by the charged areas of the latent electrostatic image, and then setting the developed image.

17. A method for producing copy comprising the steps of providing an electrically luminescent material, generat-` ing a high intensity DC field in the presence of said material, locating a doped semi-conductor layer in the area of said luminescent material, locating a layer or layers of dielectric material in the area of said luminescent material, reducing the numerical value of the intensity of said field whereby the intensity is changed to the extent that luminescence isk generated by said luminescent material, said luminescence being effective to charge the said layer to thereby produce said electrostatically charged layer, and wherein exposure of portions of said layer to radiations produces a latent image adapted to be developed to produce said copy.

18. A method for producing copy comprising the steps of providing an electrically luminescent material, generating a high intensity DC field in the presence of said material, locating a layer of chargeable material in the area of said luminescent material, reducing the numericalvalue of the intensity of said field whereby the intensity is changed to the extent that luminescene is generated andwhercin said luminescence is effective to electrostatically activate the said layer, exposing the activated `layer to radiations in selected areas whereby the charge is removed from the exposed areas to leave a latent electrostatic image in the non-exposed areas, locating an insulating overlayer upon the activated layer holding said electrostatic image, contacting said overlayer with a pigment whereby lthe pigment is adapted to be held on said overlayer in areas corresponding to said electrostatic image, and thereafter developing the image.

19. A method in accordance with claim 18 wherein said image is set on said overlayer.

20. A method in accordance with claim 18 wherein said image is transferred from said overlayer and set on a separate copy sheet.

21. A method for producing copy comprising the steps of disposing a phosphor layer between electrodes, providing an electrically luminescent material in the area of said phosphor layer, generating a high intensity DC eld between said electrodes, reducing the numerical value of the intensity of said field whereby the intensity is changed to the extent that luminescence is generated by said luminescent material and whereby the said phosphor layer becomes charged by said luminescence, exposing the charged phosphor layer to radiations in selected areas whereby the charge is removed from the exposed areas to leave a latent electrostatic image in the non-exposed areas,

locating an insulating overlayer upon the activated layer holding said electrostatic image, contacting said overlayer with a pigment whereby the pigment is adapted to be held on said overlayer in areas corresponding to said electrostatic image, and thereafter developing the image.

22. A method for producing copy comprising the steps of providing an electrically luminescent material, generating a high intensity IDC field in the presence of said material, locating a phosphor layer in the area of said 1uminescent material, locating a layer or layers of dielectric material in the area of said luminescent material, reversing said DC eld to change the intensity of said eld to the extent that luminescence is generated by said luminescent material, said luminescence being effective to thereby produce said electrostatically charged layer, and wherein exposure of portions of said surface to radiations produces a latent image adapted to be developed to produce said copy.

No references cited.

NORMAN G. TORCHIN, Primary Examiner. R. E. MARTIN, Assistant Examiner. 

1. A METHOD FOR PRODUCING COPY COMPRISING THE STEPS OF PROVIDING AN ELECTRICALLY LUMINESCENT MATERIAL, GENERATING A HIGH INTENSITY DC FIELD IN THE PRESENCE OF SAID MATERIAL, LOCATING A LAYER OF CHARGEABLE MATERIAL IN THE AREA OF SAID LUMINESCENT MATERIAL, REDUCING THE NUMERICAL VALUE OF THE INTENSITY OF SAID FIELD WHEREBY THE INTENSITY IS CHANGED TO THE EXTENT THAT LUMINESCENCE IS GENERATED AND WHEREIN SAID LUMINESCENCE IS EFFECTIVE TO ELECTROSTATICALLY ACTIVATE THE SAID LAYER, EXPOSING THE ACTIVATED LAYER TO RADIATIONS IN SELECTED AREAS WHEREBY THE CHARGE IS REMOVED FROM THE EXPOSED AREAS TO LEAVE A LATENT ELECTROSTATIC IMAGE IN THE NON-EXPOSED AREAS, DEVELOPING THE IMAGE WITH A PIGMENT WHICH IS HELD BY THE CHARGED AREAS OF THE LATENT ELECTROSTATIC IMAGE AND THEN SETTING THE DEVELOPED IMAGE. 